1. Field of the Invention
The present invention relates to a method of manufacturing a magnetoresistive device that incorporates a magnetoresistive element, and a method of manufacturing a thin-film magnetic head that incorporates a magnetoresistive element.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as the recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a write (recording) head having an induction-type electromagnetic transducer for writing and a read (reproducing) head having a magnetoresistive (MR) element for reading.
MR elements include: an AMR element that utilizes the anisotropic magnetoresistive effect; a GMR element that utilizes the giant magnetoresistive effect; and a TMR element that utilizes the tunnel magnetoresistive effect.
Read heads that exhibit a high sensitivity and a high output are required. An example of read heads that meet these requirements are GMR heads incorporating spin valve GMR elements. Such GMR heads have been mass-produced.
In general, the spin valve GMR element incorporates: a nonmagnetic layer having two surfaces that face toward opposite directions; a soft magnetic layer located adjacent to one of the surfaces of the nonmagnetic layer; a ferromagnetic layer located adjacent to the other one of the surfaces of the nonmagnetic layer; and an antiferromagnetic layer located adjacent to one of the surfaces of the ferromagnetic layer that is farther from the nonmagnetic layer. The soft magnetic layer is a layer in which the direction of magnetization changes in response to the signal magnetic field and is called a free layer. The ferromagnetic layer is a layer in which the direction of magnetization is fixed by the field supplied from the antiferromagnetic layer and is called a pinned layer.
Another characteristic required for the read head is a small Barkhausen noise. Barkhausen noise results from transition of a domain wall of a magnetic domain of an MR element. If Barkhausen noise occurs, an abrupt variation in output results, which induces a reduction in signal-to-noise (S/N) ratio and an increase in error rate.
To reduce Barkhausen noise, a bias magnetic field (that may be hereinafter called a longitudinal bias field) is applied to the MR element along the longitudinal direction. To apply the longitudinal bias field to the MR element, bias field applying layers may be provided on both sides of the MR element, for example. Each of the bias field applying layers is made of a hard magnetic layer or a laminate of a ferromagnetic layer and an antiferromagnetic layer, for example.
In the read head, in which the bias field applying layers are provided on both sides of the MR element, two electrode layers for feeding a current used for magnetic signal detection (that may be hereinafter called a sense current) to the MR element are located to touch the bias field applying layers.
As disclosed in Published Unexamined Japanese Patent Application Heisei 11-31313 (1999), it is known that, when the bias field applying layers are located on both sides of the MR element, regions that may be hereinafter called dead regions are created near ends of the MR element that are adjacent to the bias field applying layers. In these regions the magnetic field produced from the bias field applying layers fixes the direction of magnetization, and sensing of a signal magnetic field is thereby prevented. Such dead regions are created in the free layer of the spin valve GMR element.
Consequently, if the electrode layers are located so as not to overlap the MR element, a sense current passes through the dead regions. The output of the read head is thereby reduced.
To solve this problem, the electrode layers are located to overlap the MR element, as disclosed in Published Unexamined Japanese Patent Application Heisei 8-45037 (1996), Published Unexamined Japanese Patent Application Heisei 9-282618 (1997), Published Unexamined Japanese Patent Application Heisei 11-31313 (1999), and Published Unexamined Japanese Patent Application 2000-76629, for example.
It is possible to reduce Barkhausen noise while a reduction in output of the read head is prevented, if the read head has a structure such that the bias field applying layers are located on both sides of the MR element, and the electrode layers overlap the MR element, as described above. Such a structure is hereinafter called an overlapping electrode layer structure.
To improve the sensitivity of the read head incorporating the spin valve GMR element, a variety of improvements in spin valve film that make up the spin valve GMR element have been proposed. One of such next-generation spin valve films is a spin valve film in which a high resistance layer is located adjacent to one of the surfaces of the free layer that is farther from the nonmagnetic layer. (See Atsushi Tanaka et al., xe2x80x98Microstructure Process Techniques and Development of Prototype Head with Reduced Read Core Widthxe2x80x99. The 9th Research Workshop of The Second Research Division of Association of Super-Advanced Electronics Technologies, Aug. 29, 2000, pp. 65-76.) The high resistance layer of the specular spin valve film reflects electrons and thereby increases the rate of change in resistance of the spin valve GMR element. The read output of the read head is thereby increased. The high resistance layer maybe made of an oxide of a metal such as Fe, Al, Ni, or Ta.
Consideration is now given to the read head having the overlapping electrode layer structure in which the GMR element incorporating the above-described specular spin valve film is located such that the pinned layer is closer to the substrate and the free layer is farther from the substrate. To fabricate this read head, if the electrode layers are formed after the high resistance layer is formed on the free layer, the high resistance layer is located between the free layer and the electrode layers. As a result, a sense current flows from the bias field applying layers to an end of the GMR element, which results in a reduction in output of the read head and unstable operations. Therefore, to fabricate the read head that has both specular spin valve film and overlapping electrode layer structure as described above, it is necessary to adopt some method to form the high resistance layer adjacent to the free layer after the electrode layers are formed.
The following method may be taken to fabricate the read head that has both specular spin valve film and overlapping electrode layer structure.
Reference is now made to FIG. 20 to FIG. 28 to describe this method. In the method, as shown in FIG. 20, a base layer 121, an antiferromagnetic layer 122, a pinned layer 123, a nonmagnetic layer 124, a soft magnetic layer (a free layer) 125, and a protection layer 126 are formed in this order through sputtering, for example, and stacked. Each of the base layer 121 and the protection layer 126 is made of a metal material.
Next, as shown in FIG. 21, after the protection layer 126 is formed, the layers of FIG. 20 are exposed to the atmosphere, so that part of the top surface thereof is natural-oxidized and an oxide layer 140 is thereby formed.
Next, as shown in FIG. 22, a resist mask 141 is formed on the oxide layer 140 through photolithography. The resist mask 141 is used for patterning the layers from the oxide layer 140 to the pinned layer 123. Next, these layers are selectively etched through ion milling, for example, using the resist mask 141, and thereby patterned. Through this etching, part of the top surface of the antiferromagnetic layer 122 is etched, too.
Next, as shown in FIG. 23, on the antiferromagnetic layer 122, two bias field applying layers 127 are formed on both sides of the layers from the oxide layer 140 to the pinned layer 123 while the resist mask 141 is left unremoved. Each of the bias field applying layers 127 may have a structure in which a base layer 127a, a hard magnetic layer 127b and a protection layer 127c are stacked in this order.
Next, as shown in FIG. 24, the resist mask 141 is removed. The laminate in which the layers up to the bias field applying layers 127 are stacked is exposed to the atmosphere, so that part of the top surface of the protection layer 127c of each of the bias field applying layers 127 is natural-oxidized and an oxide layer 128 is thereby formed.
Next, as shown in FIG. 25, the oxide layer 140 is completely removed through dry etching. At the same time, the oxide layer 128 is removed and part of the top surface of each of the bias field applying layers 127 is removed.
Next, as shown in FIG. 26, a conductive layer 129 is formed on the bias field applying layers 127 and the protection layer 126. The conductive layer 129 is made of a material of which electrode layers 106 described later are made. The conductive layer 129 may be made up of a base layer 129a, a conductor layer 129b and a protection layer 129c that are stacked in this order.
Next, as shown in FIG. 27, a specific width of the conductive layer 129 between the two bias field applying layers 127 is etched through reactive ion etching, for example, to form a trench 130. The conductive layer 129 is divided into two by the trench 130, and the two electrode layers 106 are thus formed.
Next, as shown in FIG. 28, oxidation is performed to oxidize a portion of the protection layer 126 located in the region between the two electrode layers 106. This portion of the protection layer 126 is thereby made to have a high resistance, so that a high resistance layer 131 is formed.
Through the method including the steps shown in FIG. 20 to FIG. 28, the high resistance layer 131 is formed after the electrode layers 106 are formed.
However, the above-described method has the following problem. Through the method, the layers of FIG. 20 are exposed to the atmosphere so that part of the top surface of the protection layer 126 is natural-oxidized and the oxide layer 140 is formed. The thickness of the oxide layer 140 thus formed and the thickness of the remainder of the protection layer 126 that has not been oxidized vary, depending on the period during which the layers of FIG. 20 are exposed to the atmosphere and the temperature and humidity at which the layers are exposed. On the other hand, when etching is performed in the step shown in FIG. 25, that is, etching is performed to remove the oxide layer 140 completely, the oxide layer 140 and the protection layer 126 are etched at different etching rates. Therefore, if the thicknesses of the oxide layer 140 and the protection layer 126 vary, the thickness of the protection layer 126 that remains after the oxide layer 140 is removed varies.
When oxidation is performed in the step shown in FIG. 28, that is, oxidation is performed to oxidize the portion of the protection layer 126 located in the region between the two electrode layers 106 to form the high resistance layer 131, if the soft magnetic layer 125 is oxidized, too, a reduction in the property of the soft magnetic layer 125 results. The read output is thereby reduced. If the protection layer 126 is not fully oxidized, specular reflection of electrons in the high resistance layer 131 is not satisfactorily performed, so that it is difficult to expect an increase in read output. It is therefore desirable that only the protection layer 126 is completely oxidized through the above-mentioned oxidation.
However, if the thickness of the protection layer 126 varies, it is impossible to employ fixed conditions for the oxidation in order to completely oxidize the protection layer 126 only. If fixed conditions for the oxidation are employed, the property of the read head varies.
It is an object of the invention to provide a method of manufacturing a magnetoresistive device and a method of manufacturing a thin-film magnetic head for constantly manufacturing the magnetoresistive device and thin-film magnetic head that exhibit high outputs and high operation stability.
A method of manufacturing a magnetoresistive device or a method of manufacturing a thin-film magnetic head of the invention is provided for manufacturing the magnetoresistive device or thin-film magnetic head comprising: a magnetoresistive element having two surfaces that face toward opposite directions and two side portions that face toward opposite directions; two bias field applying layers that are located adjacent to the side portions of the magnetoresistive element and apply a bias magnetic field to the magnetoresistive element; and two electrode layers that feed a current used for magnetic signal detection to the magnetoresistive element, each of the electrode layers being adjacent to one of surfaces of each of the bias field applying layers and overlapping one of the surfaces of the magnetoresistive element. The magnetoresistive element incorporates: a nonmagnetic layer having two surfaces that face toward opposite directions; a soft magnetic layer located adjacent to one of the surfaces of the nonmagnetic layer that is closer to the electrode layers; a pinned layer, located adjacent to the other one of the surfaces of the nonmagnetic layer, whose direction of magnetization is fixed; an antiferromagnetic layer located adjacent to one of surfaces of the pinned layer that is farther from the nonmagnetic layer, the antiferromagnetic layer fixing the direction of magnetization of the pinned layer; a conductive protection layer located adjacent to one of surfaces of the soft magnetic layer that is farther from the nonmagnetic layer; and a high resistance layer that is formed through increasing a resistance of a portion of the protection layer that is located in a region between the two electrode layers.
The method of manufacturing the magnetoresistive device or the method of manufacturing the thin-film magnetic head of the invention comprises the steps of: forming the antiferromagnetic layer, the pinned layer, the nonmagnetic layer, the soft magnetic layer and the protection layer that make up the magnetoresistive element, in this order, and forming a coating layer on the protection layer, the coating layer being to be removed in a later step; forming the bias field applying layers; removing the coating layer and exposing one of surfaces of the protection layer; forming the two electrode layers on the bias field applying layers such that the electrode layers overlap the one of the surfaces of the protection layer; and forming the high resistance layer by increasing the resistance of the portion of the protection layer that is located in the region between the two electrode layers, and completing the magnetoresistive element.
According to the method of manufacturing the magnetoresistive device or the method of manufacturing the thin-film magnetic head of the invention, the sacrificial coating layer is formed on the protection layer. Before forming the electrode layers, the coating layer is removed. After the electrode layers are formed, the portion of the protection layer located in the region between the two electrode layers is processed to have a high resistance, so that the high resistance layer is formed. It is thereby possible to make the thickness of the protection layer nearly uniform when the high resistance layer is formed, and to form the high resistance layer having less variations in resistive property.
According to the method of manufacturing the magnetoresistive device or the method of manufacturing the thin-film magnetic head of the invention, in the step of removing the coating layer, the coating layer may be removed by etching, and measurement may be performed to identify an element that scatters from the coating layer by etching, and a point at which etching is stopped may be controlled, based on a result of the measurement.
According to the method of manufacturing the magnetoresistive device or the method of manufacturing the thin-film magnetic head of the invention, the step of forming the electrode layers may include the steps of: forming a conductive layer on the bias field applying layers and the protection layer, the conductive layer being made of a material of which the electrode layers are made; and forming the electrode layers by etching a specific width of the conductive layer in a region between the two bias field applying layers to form a trench so that the conductive layer is divided into two by the trench.
According to the method of manufacturing the magnetoresistive device or the method of manufacturing the thin-film magnetic head of the invention, the high resistance layer may be formed through oxidizing the portion of the protection layer that is located in the region between the two electrode layers in the step of forming the high resistance layer.
Other and further objects, features and advantages of the invention will appear more fully from the following description.